Should I use a user feedback system like UserVoice or just use a support forum?

I don't really like the idea of paying $20+ per month to run a glorified message board (GetSatisfaction, UserVoice, etc.). But these kinds of services seem to be pretty popular. So am I missing something here?

Couldn't I just modify a forum script like bbPress or Vanila to achieve the same user feedback/support functionality?

What can specialized user feedback software do that traditional forums can't?

NOTE: I'm building a simple web app like Instapaper. I don't need a team of people doing live support or anything like that.

Uservoice is not just a support forum. Besides allowing feature request/voting, it allows you as the developer to see what features are requested most. Of course not to forget you can also embed Uservoice directly to your website, making it easier for the users to give feedback.

Of course you can do all of these using a forum or even a support email. But it won't be as convenient and organized. One advantage of using a forum is that after a while, users can start helping each other.

If you are getting loads of issues/tickets/feedback, if you can afford it get Uservoice. If you are only starting out, forum will be the best and most economical way to go.

IF you like the q&a type format, consider open source alternatives like http://www.osqa.net/ or http://code.google.com/p/django-voice/ or some free services like http://www.google.com/moderator/ also allourideas has an api or widget interface for question voting.